JP4844023B2 - Dimensional stabilization method for solid polymer electrolyte membrane - Google Patents

Description

The present invention stabilizes the dimensions of the electrolyte membrane, which is the central material of MEA (electrolyte membrane-electrode assembly), which is a component of a solid polymer electrolyte membrane type (hereinafter abbreviated as “solid polymer type”) cell. It relates to the method of making. The present invention also relates to a method for storing and transporting an electrolyte membrane or MEA whose dimensions are stabilized by the method, and further to a method for producing a solid polymer cell using the electrolyte membrane or MEA. Here, “MEA (electrolyte membrane-electrode assembly)” means an electrode-electrolyte membrane obtained by joining and integrating electrodes on one or both sides of a solid polymer electrolyte membrane / ion exchange membrane. Refers to a joined body.

As shown in FIG. 1, a solid polymer type cell, typically a fuel cell, basically has one MEA (electrolyte membrane-electrode assembly), two separators / bipolar plates, A reaction gas / reaction liquid diffuser, two power supply plates, two insulation plates and two end plates, or one MEA, two separators / bipolar plates, It consists of one reactant gas / reaction liquid diffuser, one metal insoluble electrode, two power supply / current collector plates, two insulating plates, and two end plates.

By stacking one MEA, two separators / bipolar plates and two reaction gas / reaction liquid diffusers using the above components, or one MEA, two separators For example, a single cell of a fuel cell is formed by stacking a bipolar plate, a reactant gas / reaction liquid diffuser, and a metal insoluble electrode. A plurality of single cells are stacked to form a cell stack. A power supply / current collector plate, an insulating plate, and an end plate are arranged at both ends of the cell stack, and the bolts provided on the end plate are tightened to form the shape. The fuel cell is configured in the manner of maintaining.

In the cell configuration, an example in which an MEA and a diffuser are integrated can be seen (Patent Document 1). However, this type of cell including a fuel cell basically has a threshold of MEA or electrolyte membrane. An electrochemical reaction apparatus having two isolated reaction chambers between two separators / bipolar plates, with two electrodes so that the reactant / product can be handled in the case of gas A structure in which at least one of them is a gas diffusion electrode is more general.

The polymer electrolyte cell having such a structure is referred to as a water electrolysis cell, a reversible cell (integrated fuel cell and water electrolysis cell, “integrated renewable fuel cell” URFCS) in addition to various fuel cells. ), Dehumidification cell, oxygen concentration cell in air, soda electrolysis cell with oxygen cathode, on-site ozone or hydrogen peroxide production cell, nitrous acid gas, Freon gas, carbon dioxide It is an electrochemical cell that is expected to be used in a wide variety of applications, such as an electrochemical cell.

In these polymer electrolyte cells, if the scale of the cell is increased by increasing the size of the single cell, the restriction on the processing accuracy associated with the increase in the size of the component will increase, and the components will be uniform when tightened. We encounter problems such as difficulty in obtaining contact. Scale-up by increasing the size of a single cell also increases the electrolysis current and power generation current. As a result, there is a problem that the efficiency of the entire system decreases due to an increase in voltage drop and a decrease in rectification efficiency of the power supply device. is there. Therefore, as shown in FIG. 1, it is usual to increase the scale by a cell stack in which single cells are stacked.

The formation of transport paths for reactants and products / by-products in single cells and stacks of such polymer electrolyte cells is an “external manifold system” in which an external introduction path is provided for each cell. Or a space formed by stacking openings provided in the constituent members is used as a main line of the header pipe structure, and a mechanism for branching out of each single cell from there is provided in the cell. According to one of "method". Usually, an internal manifold system is selected which is advantageous in terms of cost reduction and space saving due to simplification of the structure.

In the internal manifold system, the reactants supplied from the outside first flow into the cell chambers from the flow dividing mechanism provided in each cell through the internal manifold, and pass through the flow path provided on the separator. Since the reactant fluid flows out to the diffuser side and permeates there to reach the electrode surface, two or more kinds of reaction fluids are formed in the two isolated reaction chambers formed in the cell as described above. When supplying different reactants, it is necessary to provide an internal manifold for each chamber. Basically, a total of four openings are provided for the entrance and exit of the reaction gas A and the entrance and exit of the reaction gas B. However, when the reaction system is exothermic and the introduction of coolant is necessary, When the number of cells reaches several tens to several hundreds, it is necessary to additionally provide an internal manifold for the cooling system entrance / exit.

In order to allow the intended electrode reaction to proceed continuously in a safe and stable manner in a stack that employs an internal manifold system, the manifolds are separated from each other, for example, by inserting an appropriate sealing material. Thus, the reactants, products and coolant must be kept from mixing with each other.

In order to form an internal manifold having the above functions by laminating constituent members, it is necessary to provide openings at corresponding locations on the MEA / electrolyte membrane, separator / bipolar plate, and power supply plate. Otherwise, the reactants and cooling water will mix and the cell stack will not be able to perform its function. Therefore, high processing accuracy of the manifold openings of the constituent members, particularly that the pitch of the opening holes is uniform, is essential for the production of the solid polymer cell. In particular, with respect to the MEA and the separator, as shown in FIG. 2, dimensional consistency is maintained between the opening provided in the MEA and the electrode part, and between the opening provided in the separator and the flow path / electric contact surface. Therefore, higher machining accuracy is required.

However, the solid polymer electrolyte membrane has a moisture content that changes with changes in temperature and / or humidity, and changes in dimensions accordingly. The dimensions of the dry state and the fully swollen state in water vary by about 20%, although there are some differences depending on the ion exchange capacity of the electrolyte membrane and the type of ion exchange group. Indicates. For this reason, even if the opening of the manifold opening is performed after the MEA is manufactured, if the MEA is left as it is, the opening is shifted immediately after the processing, and the opening of the MEA, the electrode, and the separator are opened. Dimensional mismatch between the liquid crystal part and the flow path part / electric contact part, leading to a situation where it cannot be incorporated into the cell. This problem occurs not only between the manufacturing stage and the cell assembly operation, but also during storage and transportation.

Due to the dimensional instability of such a solid polymer electrolyte membrane, the electrolyte membrane is almost perfect in the actual usage environment even when the cell is assembled using carefully managed equipment. Therefore, it is difficult to avoid swelling. If the electrolyte membrane expands, wrinkles approach the portion that is not tightened with a bolt or the like, as shown in FIG. According to the inventors' experience, the wrinkles reach a height of about 0.5 to 1.0 mm. If it does so, an electrolyte membrane will fall into a channel of about 1 mm in depth provided on a separator, and a channel will be narrowed or it will be blocked if it is severe. This is also confirmed from the phenomenon that the pressure loss between the inlet and outlet of the cell increases.

As long as the expansion of the electrolyte membrane cannot be prevented, it is difficult to control the generation of wrinkles and the shape of the wrinkles in the membrane. If the flow path is narrowed or blocked by wrinkles, the flow resistance of each cell that makes up the stack will vary, so the reactant fluid supply from the manifold to each cell will be irregular, and the stack performance will vary. However, as a problem before that, it becomes difficult to manufacture a cell stack with high reproducibility. For this reason, there is a need for measures to stabilize the dimensions of the electrolyte membrane for the polymer electrolyte cell and the MEA.

As a measure therefor, it is conceivable to first produce a solid polymer electrolyte membrane with little variation in dimensions, and techniques for realizing it by improving the production method have been disclosed (Patent Documents 2 to 4, Non-Patent Document 1). . On the other hand, it is possible to prevent moisture from evaporating from the electrolyte membrane during the thermocompression bonding process between the electrode and the electrolyte membrane to maintain the electrolyte membrane in a wet state (Patent Document 5), A countermeasure for activating the MEA after incorporation (Patent Document 6) has also been proposed. However, these are not techniques for stabilizing the dimensions at the time of manufacturing the electrolyte membrane or MEA or after processing the opening, and thus do not have the effect of preventing the above-described deviation of the opening pitch and generation of wrinkles.
Japanese Patent Application No. 2002-295311 JP 2003-297393 A JP 5-75835 JP-A-6-231777 JP 10-40932 A JP2004-6416 Wakizoe et al. "Study on ion exchange membrane for solid polymer fuel cell" Proceedings of Fuel Cell Symposium (1997)

A basic object of the present invention is to provide a method for stabilizing the dimensions of a solid polymer electrolyte membrane which is a constituent member of a solid polymer cell. The practical purpose of the present invention is to prevent the pitch deviation of the openings provided in the electrolyte membrane and MEA by stabilizing the dimensions of the electrolyte membrane, and to prevent the electrolyte membrane from wrinkling during use. For the purpose of facilitating assembly, storage and transportation of cell stacks, preventing narrowing and blockage of flow paths, and thereby enabling the production of stable and highly reliable polymer electrolyte cells. Yes. It is also included in the practical object of the present invention that the dimensional stabilization of the MEA and the electrolyte membrane that have been processed for the opening can be carried out by simple equipment for their transportation, storage, and assembly operations. .

Dimensional stabilization method of the electrolyte membrane of the present invention is a method of stabilizing the dimensions of the solid polymer electrolyte membrane which is a component of a polymer electrolyte cell, in principle, a solid polymer electrolyte membrane, In a state immersed in pure water, dilute acid solution or alkali solution, the solid polymer electrolyte membrane is expanded as much as possible by heat treatment at a temperature not higher than 100 ° C. but exceeding the operating temperature of the solid polymer electrolyte membrane. In the case of treatment with a dilute acid or alkali solution, the treatment is followed by washing with pure water and maintaining the wet state at a temperature not higher than the temperature at the end of the treatment until the point of use. More specifically, the dimensional stabilization treatment is performed on the solid polymer electrolyte membrane incorporated in the electrolyte membrane-electrode assembly.

The dimensional stabilization of the solid polymer electrolyte membrane by the method of the present invention makes it possible to eliminate or reduce the dimensional irregularity of the solid polymer electrolyte membrane by a simple method. Specifically, the dimensional change that occurs in the MEA or the electrolyte membrane can be suppressed to within 2%, and by selecting the treatment temperature in the expansion treatment to be higher than the actual cell use temperature, It is possible to substantially suppress the generation of wrinkles generated in the cell. Naturally, the object of stabilization includes solid polymer electrolyte membranes that are currently commercially available and available. Because of these effects, using a simple manufacturing facility, while preventing the deviation of the opening hole pitch provided in the solid polymer electrolyte membrane or MEA and the generation of wrinkles that occur during use, the solid polymer cell Can be reliably manufactured.

In the polymer electrolyte cell manufactured by the simple technique, the generation of wrinkles in the electrolyte membrane can be prevented, and the functional requirement that the flow path in the internal manifold is not blocked or leaked is sufficiently satisfied. Although it has been considered that handling of the MEA or the electrolyte membrane in which the opening has been processed is difficult, the transportation and storage thereof can be similarly performed easily and easily. Actually, after the expansion process is performed first, the opening is processed, and then stored and transported by immersing it in deionized pure water, dilute acid, or alkaline solution, which is lower than the temperature during the expansion process. Since only a dimensional change of 2% or less occurs as described above, it is easy to store and transport the electrolyte membrane and MEA in an ideal state. Even when stored for a long period of time, if necessary, if a treatment with a dilute acid or alkali solution below the expansion treatment temperature or a washing treatment with pure water is carried out again before use, no dimensional problem will occur.

In the present invention, the relationship between the dimensions and the water temperature of the solid polymer electrolyte membrane and MEA to be dimensionally stabilized is shown in Table 1 (electrolyte membrane) and “Naffion 115” as an example. It is as Table 2 (MEA). A to N in Table 1 and 1 to 14 in Table 2 mean that the water temperature history was changed with time according to the numbers, respectively, and the expansion rate was 10 minutes at 140 ° C. for the electrolyte membrane and MEA. It is the value which showed the increase rate of the dimension in each water temperature calculated | required on the basis of the dimension of what was dried (1.0). For these properties of solid polymer membranes, see “Electrochemistry and Industrial Physical Chemistry” (1984) p. The data of Table 1 and Table 2 are the results of experiments conducted by the inventors based on the suggestions.

Table 1 Dimensional change of solid polymer electrolyte membrane with water temperature

Table 2 Dimensional change of MEA with water temperature

From the data in Table 1, the following can be seen as basic properties of the solid polymer electrolyte membrane.
(1) The dimensions increase when moving from a dry state to a wet state.
(2) The size in water increases monotonously up to around 100 ° C. as the water temperature rises.
(3) Once the temperature is increased to 60 ° C., 85 ° C. and 100 ° C. and expanded, the dimensions reached will no longer change even when the water temperature is lowered to 20-5 ° C., and return to the original dimensions. Absent.
(4) However, once expanded in a wet state, the size shrinks and shrinks when dried.

Specifically, the processing method of the present invention for stabilizing the dimensions by utilizing the properties of the above-mentioned solid polymer electrolyte membrane is specifically designed by placing one to several tens of solid polymer electrolyte membranes or MEAs in a container. It is immersed in an aqueous solution of deionized water, dilute acid or alkali, and the solution is heated and placed at a temperature higher than the maximum use temperature of the intended solid polymer cell for at least 20 minutes.

As a container used for processing, a material which does not allow elution of anions and cations which may be mixed as a contaminating component, such as Pyrex glass, high density PP, high density PE, heat resistant polyvinyl chloride, PTFE, etc. A metal container lined with a polymer is preferable. Prior to use, it is preferable that the inside of the container is washed with pure water to remove impurity ions, and the conductivity of the washing water is 5 μS / cm or less.

Since it is desirable that the temperature distribution in the bath is uniform during the treatment, a stirrer or a circulation pump may be used. In order to obtain the desired dimensional stability, the bath setting temperature during the treatment may be any temperature as long as it is basically higher than the maximum use temperature of the cell. However, the heat resistant temperature of the solid polymer membrane used is not limited. Is the upper limit. Considering the accuracy of the measurement system, the size of the bath, the temperature distribution in the bath, etc., the dimension can be stabilized without problems if the temperature is raised 5 ° C. or more from the maximum operating temperature.

If heat processing is performed, the temperature of a liquid will be reduced to the range of 5 degreeC-room temperature, with electrolyte membrane or MEA being immersed in the liquid in a container. When an aqueous solution of dilute acid or alkali is used as the treatment liquid, the electrolyte membrane is taken out from the liquid and washed with deionized water. Cleaning is performed until the conductivity of the cleaning liquid is 5 μS / cm or less. Usually several washings are enough. The solid polymer membrane once expanded shrinks when dried, so the electrolyte membrane or MEA should not be removed from the bath until the above cooling is complete, but once cooled to near room temperature, the water evaporation rate is sufficient. Drying and shrinkage are practically no problem.

In the processing of the electrolyte membrane or MEA taken out from the container, holes are made at predetermined locations while supplying deionized water so that the electrolyte membrane does not dry. There are no particular restrictions on the processing tool. In order to ensure certainty, it is desirable to use a device that ensures that the solid electrolyte membrane is always immersed in deionized water, or at least a processing device that has a mechanism that hardly causes evaporation of water. For example, an electrolyte membrane or MEA is fixed to a jig as shown in FIG. 4, deionized water is injected, and the flat plate is stretched while preventing evaporation of water by the holding plate shown in FIG. 4. In this state, if an opening is provided at a predetermined location using a tool, the electrolyte membrane or MEA can be processed without any change in dimensions.

To store and transport an electrolyte membrane or MEA that has been processed for an opening without dimensional change, select a container or storage location that can maintain a water temperature of 5 ° C. to a heat treatment temperature or lower, and store the electrolyte. It is only necessary that the membrane or MEA is always immersed in deionized water. During transportation, a sufficient amount of deionized water is poured into a bag or container of PE, PP, etc. that has been washed with deionized water until the cleaning solution reaches 5 μS / cm or less, and an electrolyte membrane or MEA is placed therein. It should be sealed and kept at a temperature not exceeding 5 ° C. to the processing temperature. If the storage location greatly exceeds the room temperature or reaches a high temperature that greatly exceeds the room temperature during transportation, if the temperature of the heat treatment is set in consideration of the temperature, the dimensional change of the electrolyte membrane and MEA is accompanied. It can be stored and transported.

The assembly of a polymer electrolyte cell stack using a dimensionally stabilized electrolyte membrane or MEA is performed by pre-immersing the separator in deionized exchange water to retain moisture, and the separator A / diffuser / opening processed MEA. Alternatively, the components may be laminated like the electrolyte membrane / diffuser / separator B. In order to prevent the MEA and the electrolyte membrane from drying and shrinking during the lamination, the work may be performed while pouring deionized water onto the MEA and the electrolyte membrane. In order to supply water to the cell located below the laminated body, there is a method of temporarily pressurizing the laminated body with a press and using an internal manifold formed at that time. After stacking a number of parts corresponding to a predetermined number of cells, a bolt on the end plate is tightened to finally form a solid polymer cell stack having an arbitrary number of cells, for example, 10 cells.

The type of the solid polymer electrolyte whose dimensions can be stabilized by the method of the present invention is not limited, and has a group such as —NH ₄ ⁺ , —COO ⁻ or —SO ₃ ^{2 —} as an ion exchange group. However, those that retain hydration water and increase in size due to the incorporation of hydration water, and those that have the property of increasing the amount of water incorporation by increasing the bond distance between molecules due to an increase in temperature. These are the objects of dimensional stabilization according to the present invention.

However, the type of bath that can be used or is suitable is limited depending on the type of the solid polymer electrolyte. For example, for those having a strongly acidic type —SO ₃ ^{2 —} group, strong acids such as dilute sulfuric acid and dilute hydrochloric acid can be applied in addition to deionized water, but those having a weakly acidic type —COO ^— group In deionized water, deionized water and an alkaline solution can be used for those having —NH ₄ ⁺ groups. A bipolar membrane obtained by joining an anion membrane and a cation membrane also advantageously uses deionized water.

The possible MEA that can be dimensionally stabilized by the method of the present invention is not limited in its type, manufacturing method, and the like, and any of the hot press method and the electroless plating method can be used. The data shown in Table 1 and Table 2 is that of MEA in which a water repellent material is contained in the catalyst layer, but even if the electrode surface itself has water repellency, the method of the present invention It can be seen that it is sufficiently applicable.

However, since the expansion ratio of the electrode area differs depending on the MEA manufacturing method, the dimensional stabilization process according to the present invention is performed, and in order to realize a MEA having a predetermined effective electrode area, the electrode area at the time of manufacturing the MEA, It is necessary to obtain a relationship with dimensions after processing at a predetermined temperature, and to manufacture the electrodes with a slightly smaller size based on the relationship. What is necessary is just to design the catalyst load per unit area of an electrode so that it may become a required quantity with respect to the electrode area after a stabilization process. The portion on the MEA where the electrode is not covered exhibits the same properties as a normal solid electrolyte, and therefore there is no particular problem and the present invention can be applied.

Regarding the electrolyte membrane and MEA processed as described above, when contamination occurs due to the tool, processing atmosphere, and storage environment, particularly when there is a possibility that the adsorption of impurity ions to the ion exchange group has occurred, After any of the operations described with reference to FIG. 4, impurity ion desorption treatment using a strongly acidic solution or an alkaline aqueous solution can be performed subsequently. Then, if it treats with deionized water, it can use for the assembly of a cell without a problem. Also in this case, if the temperature of the solution to be used is controlled so as not to exceed the temperature selected from the range of 5 ° C. to the maximum use temperature, the dimensional change of the solid electrolyte or MEA can be prevented.

N ₂ gas was sealed at a pressure of 50 kPa in one of a total of four reaction gas and cooling water manifolds of the manufactured 10-cell stack, and it was confirmed that there was no leak. Furthermore, a cell stack using a Pt catalyst for the bipolar electrode catalyst layer of the 10 cell stack MEA was manufactured, and pure H ₂ , pure O ₂ and humidified water vapor were introduced into two systems of the reaction gas manifold. If the internal manifolds formed in the manufactured cell are not sufficiently divided or the electrolyte membrane is damaged, hydrogen and oxygen will be mixed, and there will be no difference in concentration between the two electrodes. The phenomenon that the cell voltage shows a voltage in the vicinity of 0V without polarization or the voltage value greatly increases or decreases below 0.8V occurs. With respect to the manufactured stack, as shown in Table 3, an open circuit voltage of about 1 V was obtained in all the cells, and it was confirmed that each internal manifold was divided.

Table 3 Open circuit voltage cell of each cell when hydrogen-oxygen is introduced into the cell stack of the present invention

Reference example

A three-cell stack was manufactured in the same manner as in Example 1, and the dry N ₂ gas was circulated while maintaining the stack temperature at 68 ° C., and the AC resistance value at 1 kHz of the LCR meter was measured between the stack terminals. The MEA was dried until the resistance value increased from 2.22 mΩ to 290 mΩ.

The fuel cell was operated by placing the MHA that had been dimensionally stabilized according to the present invention in the cell. When the cell was disassembled after drying the MEA by the above method, the MEA suddenly contracted in size immediately after disassembly. For this reason, even if it is inserted into the cell, it is clear that the MEA contracts if exposed to the drying conditions. I was worried about the situation.

On the other hand, the drying operation was carried out three times while measuring the resistance value, and then H ₂ , O ₂ and humidified water vapor were introduced into the two systems of the reaction gas manifold, respectively. An open circuit voltage of about 1V was obtained. From this, it was confirmed that even when the MEA contracts due to drying, the MEA or the electrolyte membrane is not damaged due to insufficient strength, and the threshold of the internal manifold portion can sufficiently function.

Table 4 Open circuit voltage of each cell upon introduction of hydrogen-oxygen after repeated drying of the stack

The results shown in Table 3 indicate that the method of operating a cell equipped with a solid electrolyte or MEA that has been dimensionally stabilized according to the present invention, in particular, using a gas diffusion electrode and reacting gas to the electrode surface. If wetting of the cell becomes a problem, a dry fluid such as N ₂ is introduced after the cell is manufactured to remove a large amount of water introduced into the cell at the time of manufacturing. This is the fact that this method is effective.

The cell with MEA treated according to the present invention was disassembled and the MEA was observed. As shown in FIG. 3, almost no wrinkles were observed on the MEA. This observation result is consistent with the fact that the pressure loss is suppressed according to the present invention in the data of Table 4 in which the pressure loss (flow resistance) in the cell is measured. It was confirmed that it was avoided.

Table 5 Pressure loss in polymer electrolyte cell

The schematic diagram which shows the general structure of a polymer electrolyte fuel cell. The typical figure which shows the connection of the electrode part and opening part on MEA, and the power-saving part / flow-path part and opening part on a separator. The photograph which compared the external appearance after use of MEA (a) which gave the dimensional stabilization method of this invention, and MEA (b) which does not give. Explanatory drawing of the process which processes the opening part of MEA / electrolyte membrane

Claims (5)

A method for stabilizing the dimensions of a solid polymer electrolyte membrane, which is a component of a solid polymer cell, comprising a solid polymer electrolyte membrane incorporated in an electrolyte membrane-electrode assembly (hereinafter abbreviated as “MEA”) , In a state immersed in pure water, dilute acid solution or alkali solution, the solid polymer electrolyte membrane is expanded as much as possible by heat treatment at a temperature not higher than 100 ° C. but exceeding the operating temperature of the solid polymer electrolyte membrane. In the case of treatment with a dilute acid or alkali solution, the treatment is washed with pure water following the treatment, and the wet state is maintained at a temperature below the temperature at the end of the treatment until the point of use. . The method according to claim 1, wherein the dimensional stability is such that the dimensional variation rate of the solid polymer electrolyte membrane in the temperature range of 5 to 100 ° C is 2% or less. The MEA incorporating the solid polymer electrolyte membrane that has been subjected to the method according to claim 1 and whose dimensions are stabilized is stored or transported in a state of being immersed in pure water within a temperature range of 5 to 100 ° C. A method for storing or transporting a dimensionally stabilized solid polymer electrolyte membrane, comprising: A solid polymer type comprising: subjecting a MEA incorporating a solid polymer electrolyte membrane having a dimension stabilized by performing the method according to claim 1 to perforating and assembling a solid polymer type cell stack. Cell manufacturing method. A solid polymer cell comprising , as a constituent part , an MEA incorporating a solid polymer electrolyte membrane that has been subjected to the method according to claim 1 and whose dimensions have been stabilized.

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